From time to time, fatal accidents occur due to an aerial vessel, specifically a helicopter, coming into contact with overhead cables such as power lines and telecommunication cables. Specifically, it is a challenge to avoid such overhead cables during landing of the aerial vessel in terrain unfamiliar to the pilot.
Often, overhead cables have such small dimensions (small width) that they are difficult to observe with the naked eye.
Traditionally, helicopter crews have avoided overhead cables by using maps in which known overhead cables are drawn in.
Consequently, within the field, there exists a general need for methods and devices to detect overhead cables from an aerial vessel.
Previously, overhead cables have been detected from an aerial vessel, based on use of a camera and image processing techniques processing the image shut by the camera.
For example, EP-1 908 010 shows a system and a method for passive detection of cables from a helicopter. A digital image is captured from the helicopter. Firstly, the digital image is pre-processed to reduce noise which does not resemble cables. Then pixels are identified which may be classified as cables using a segment-finder module. Further, the identified pixels are linked in a linker module, to determine if a cable-like structure is present. This generates a cable overlay. The linker module comprises spatial and temporal filters. The spatial filter eliminates features in the image which are not consistent with cables, while the temporal filter eliminates pixels which do not fulfill a minimal image-to-image persistence. When a cable is detected the pilot is warned.
In such warning systems it is desirable to improve the safety to insure that warning is given when an overhead cable is actually present. At the same time, it is desirable to avoid a warning when an overhead cable is not present.
One or more embodiments of the invention provide an improved method and device for detecting overhead cables from an aerial vessel.